1. Field of the Invention
Bovine mastitis is a serious problem, common in both lactating dairy-type and beef-type animals. The management of this disease is practiced mostly on the dairy-type animal where daily udder handling and treatment is readily accomplished. Mechanical milking machines may have caused an increased incidence of mastitis; the true origins of the disease remain unknown. Bacterial organisms identified from affected glands are varied; however, the species of streptococcus and staphlococcus are most commonly isolated.
Good animal husbandry practice offers a lower general indidence of mastitis. Antibiotics and chemotherapeutic agents have also demonstrated advantage in restoring affected animals back to healthy milk production. Vaccination has been shown to be useful in minimizing mastitic attack in dairy goats; however, it has not been demonstrated to be useful in cattle.
The control of mastitis in milk-producing animals is, therefore, relegated to good management, selected animals, and medicinal agents. The medications are used both for acute mastitic outbreaks and as prophylactic remedies as dry cow preparations. Of special significance are dosage forms which release the medication in a sustained manner over several days, enabling the complete eradication of the causative organism and guarding against reinfection from the contaminated environment.
A major use for such dosage forms is in dry cow treatments, that is during the approximate 4-week to 10-week period of time immediately preceding the delivery of a calf. The delivery time is also known as the time of freshening, suggesting the new lactation cycle. A treatment approach during the dry period, nonlactating time, reduces the potential of contamination of the milk supply by medicinal agents and provides what should be an effective time exposure of the medication in the udder tissue.
2. Description of Prior Art
Present products available are formulations of medicaments in aqueous, glycol, or vegetable oil-type vehicles. For more prolonged release of medicaments in the udder, mineral oil and vegetable oil with gellants such as amorphous silicon dioxide, aluminum stearates, and emulsifier-type agents are used. The capability for varying the composition of the presently employed ingredients to provide for long term release of medication is limited. The release of the medication relies on its physical liberation from the nonwater soluble and nonerodible vehicle and, thus, is not subject to accurate control in the udder.
A further drawback of present mastitis treatment formulations is that they may harbor pathogenic organisms. Some formulations are sterile to obviate this hazard, others may be pasteurized, and still others may pay no regard to this problem. Enteric pathogenic organisms have been isolated from mineral oil, peanut oil, and other pharmaceutic oils. To minimize problems of this type, preservatives, e.g., chlorobutanol, have been employed.
A further drawback of present formulations, which are based on nonerodible vehicles such as mineral oil, is that these vehicles may persist in the udder or find their way into the milk supply.